It is well known in the art that a display device having a screen provided by arranging incandescent lamps in matrix form may be used as the score board of a baseball field or a stadium or on an advertising pillar. In some display devices, pictures are displayed as seen in television sets. Also in some display devices, characters, messages and pictures are displayed in superposition. In this case, in general, in a conventional display device of this type, character data and a video signal are mixed to provide a composite video signal (including synchronizing signals), and the composite video signal is stored in a frame memory, and is then processed as required for display. Accordingly, the editing operation is troublesome, taking a lot of time.